Astronomy
Earth

An Asteroid We Saw Coming

Published on 25 November 2022

On November 19, the little asteroid 2022 WJ1 burned up as it entered the atmosphere over North America. It had been detected a few hours before the event by an automatic telescope monitoring the sky.

Every day, our planet is “bombarded” by wandering pebbles from the sky. The vast majority of these objects are the size of specks of dust and are almost entirely burned up in the atmosphere due to their high entry speed. This natural shield is effective for objects of up to about 7 to 10 m wide.

2022 WJ1: The Sixth Asteroid Detected Before its Arrival

Much larger asteroids have the potential to cause disasters upon impact with Earth. This is why observatories have been created equipped with automatic telescopes which scan the sky in order to detect the most dangerous. To date, more than 30,000 Near-Earth Objects have been identified. Near-Earth Asteroids are asteroids whose orbit approaches that of the Earth.
Initially these observatories were designed to identify objects of 1 km and over which, in the event of a collision, would mean the end of our civilisation. Fortunately, there are none at the moment. But the performance of these observatories has evolved to the point where they can now detect much smaller asteroids, and sometimes before they enter our atmosphere.

One of the Catalina Sky Survey telescopes in Arizona that detected Asteroid 2022 WJ1.
© University of Arizona

The spectacular “shooting star” caused by asteroid 2022 WJ1 entering the atmosphere on November 19, 2022. The
photo was taken by astronomer Robert Weryk from Ontario, Canada.
© Robert Weryk

This was the case for 2022 WJ1 detected on November 19 by the Catalina Sky Survey in Arizona at 04:53 Universal Time. Three more sightings followed, providing enough data for European Space Agency (ESA) software to calculate an impact risk of about 20 % within 2 to 3 hours. Very quickly, dozens of additional observations (a coordinated global network exists) refined the result and 2022 WJ1 burned up as it passed over Lakes Erie and Ontario, not far from the Canada – United States border. The asteroid having an estimated width of 1 m, it presented no danger . This is the sixth time that automatic sky monitoring telescopes have detected an asteroid before it entered our atmosphere.

A Logic of Planetary Protection

Space agencies and astronomical institutions have thus set up over the years a real logic of planetary protection. ESA has its own body called the Near-Earth Object Coordination Center (NEOCC). For NASA, this is the Planetary Defense Coordination Office (PDCO).
The goal most often publicised by these organisations is to detect an asteroid likely to cause destruction on a planetary scale and to carry out a deflection mission. While the possibility of this scenario is indeed being studied, and was even the subject of a feasibility test recently with DART, the protection of our planet is also focusing on smaller asteroids, damage caused by which could affect large areas such as cities or regions.

Such “wandering pebbles” (tens of metres or a hundred metres wide) could unfortunately sometimes be perceived too late for a space mission to be launched in time (their small size makes them difficult to detect).

On the other hand, technical progress makes it possible to envisage spotting them early enough for an alert to be initiated, followed by an evacuation of the populations of the threatened region. NASA also finances ATLAS-type observatories (Asteroid Terrestrial-impact Last Alert System), specifically designed by the University of Hawaii to search the sky for this type of asteroid.
At Cité de l’ espace in Toulouse, the IMAX film Asteroid Hunters 3D tells the story of all of this general approach to protecting the Earth.

Below is a video explaining (in English) how ATLAS works.

Calculation by ESA of the re-entry corridor of the asteroid 2022 WJ1 over North America.
© ESA

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